Telephone system



March 31, 1942.

T. L. DIMOND TELEPHONE SYSTEM Filed Oct. 29, 1940 3 Sheets-Sheet l I/VI/EN TOR 7T L. DIMOND mcmm AT TORNEV March 31, 1942. T, L, mMOND 2,278,172

TELEPHONE SYSTEM Filed Oct. 29, 1940 3 Sheets-Sheet 2 TRUNK RELEA SE CIkCU/T m/ l/EN TOR 7? L. DIMOND A T TOP/V5) Patented Mar. 31, 1942 TELEPHONE SYSTEM Thomas L. Dimond, But to Bell Telephone Lab herford, N. J., assignor oratories,- Incorporated,

New York, N. Y., a corporation of New York Application October 29, 1940, Serial No. 363,265 12 Claims. (01. 179-457) This invention relates to telephone systems and particularly to systems comprising unattended automatic ofiices.

It is the object of the invention to improve the facilities provided in telephone systems for transmitting alarms from anun-attended dial office to the master ofiice and to increase the efficiency of trunking systems.

It is usual to provide alarm apparatusin an unattended dial oifice which is efiective when a trouble condition exists to seize a trunk through which calls tothe master office may be completed and upon answer of the call in the master oflice to transmit a tone signal to indicate that the call is an alarm call from an unattended omce. The patent to J. N. Walters No. 2,262,595 granted Nov. 11, 1941, discloses a system comprising an unattended ofiice having direct trunks to a master ofiice and alarm apparatus for seizing either one of two of these trunks. for transmitting trouble signals thereover. When, however, calls from a first unattended dial office toa master office are completed through a second or tandem unattended office, seizure of a trunk in the first unattended ofiice on a call to the master ofice may effect the automatic operation of an incoming selector in the tandem office to select an idle trunk from the tandem ofiice to the master office. Such a system is disclosed in the patent to J. Baumfalk et al. No. 2,268,635 granted Jan. 6, 1942. If all-of the trunks to the master oifice are busy, upon seizure of a trunk in the first unattended office on a call to the master office, a busy tone is transmitted to the first unattended oflice;

and, if the call is from a subscriber, theconnection will be released in usual manner.

But if the call is a trouble alarm call, the tone signal is inefiective to cause release and the trunk will be held without completion of the alarm call.

This invention is an arrangementv which provides for the automatic release of a trunk seized in an unattended office on a trouble alarm call to the master office in case the call is not -an swered within a predetermined interval of time after seizure of the trunk.

According to a. feature of the invention automatic release means is provided in an unattended dial Office for the trunks which are seizable on trouble alarm calls to the master ofiice; the

release means, comprising a relay for each of the trunks, being effective to release a trunk seized on an alarm call if they call is not answered within a predetermined interval of time.

According to another feature of the invention automatic trunk release means is provided in an unattended dial office, said release means being common to the trunks. which are seizable on trouble alarm calls to the master ofiice.

A clear and complete description of the invention and its features will be facilitated by considering a telephone system in.which the invention is embodied, such a system being shown schematically in the drawings which form a part of this specification. The invention is not limited in. its application to the particular system shown in thedrawings but is generally applicable to automatic switching and signaling systems.

' Referring to the drawings:

Fig. 1 shows an unattended dial ofiice LO comprising subscribers stations A and B, lines Ll and L2, line circuits. LCI and L02, line-finder switch LFI, first selector SI, and a connector CI;

Fig. 2 shows alarm apparatus MA in the unattended office. LO;

Fig.3 shows an alternative arrangement of the alarm apparatus MA in the unattended office L0;

and

Fig. 4 shows trunk circuits TCI and T05 in the unattended ofilce LO; shows a tandem unattended ofiice comprising trunkcircuit TC2, incoming selector IS andxtrunk circuit T03; and shows a master office comprising a trunk circuit TC4 terminating at a jack J at an operators position.

The subscribers stations are of the type provided on lines terminating in common battery central offices and each includes a dial or other impulse sender for controlling the operation of automatic switches through which desired connections are established. The line-finder, selector and connector switches maybe of the wellknown two-motion step-by step type. Reference may be had to Automatic Telephony by. Smith and Campbell, 2nd edition, pages 53 to 65, inclusive, for a description of the structure of such switches and their operation when used as solectors and connectors. The line circuits LCI and L02 may be similar to the linecircuit disclosed in the patent to T. L. Dimond No. 2,210,- 068, granted August 6,, 1940; and reference may be had to this patent for a description of the operation of a two-motion step-by-step line finder. The line finder LFI and the connector Cl are each represented by a set .of brushes and a single set of terminals, all operatingmagnets and control relays being omitted. The selector SI is represented by a set of brushes, by a set of terminals 35 representing a level through which the selector has access to connectors CI, and by two sets of terminals 31 and 88, representing the tenth level of the bank through which the selector has access to trunks to the tandem ofiice on calls to an operator in the master ofifice; all operating magnets and control relays associated with selector SI are omitted.

The alarm apparatus MA in Fig. 2 is similar to the alarm apparatus MA disclosed in the aforementioned patent to J. N. Walters except that relays I81, I91, I98, I8I and I03 and resistors I88, I98 and I02 have been added to effect the automatic release of either of the trunks used for alarm calls as hereinafter described in detail. The apparatus MA is represented by alarm relays HI and I12 which are operated upon the occurrence of trouble conditions; relays I13, I14 and I16, for initiating an alarm call and for preventing a second alarm call after answer and release of a first alarm call when the trouble condition continues to exist; relays I85, I86 and I 81 individual to one of two trunks connected for use on alarm calls; relays I95, I96 and I91 individual to the other of these trunks; and relays I80, NH and I03 for effecting release of a seized one of the two trunks in case the call is not answered within an interval of from two to-eight minutes after seizure.

The alarm apparatus MA shown in Fig. 3 is similar to that disclosed in-the aforementioned patent to J. N. Walters, except that relays I85 and I96 are added to control the automatic release of either of the two trunks used for alarm ca s.

The ringing and tone apparatus RA comprises a start relay and a tone transformer LTI which supplies the trouble tone which is transmitted on an alarm call to the master office. Timing relays I I I, H2 and H3 operate in a two to four-minute cycle to periodically connect ground to and disconnect ground from conductors H4 and H5 as long as ground is connected to start conductor III].

The trunk circuit TCI associated in ofiice LO with one of the two trunks which are used for alarm calls, in addition to being used for regular calls, comprises a repeating coil RCI, line relay 90, release control relays 86 and 81, pulse generating relays 14, 88 and 89, an outgoing call control relay 82, and a polarized supervisory relay 84. The trunk circuit T05 associated with the other of the trunks used for alarm calls is similar to trunk circuit TCI. The trunks TI and T5 are two-way trunks but the relays used only on incoming calls are not shown in Fig. 4. Reference may be had to the aforementioned patent to J. Baumfalk et al. for a complete detailed disclosure of the trunk circuits TCI and T05.

The trunk circuits T02 and TC3 in the tandem office and trunk circuit TC4 in the master ofiice are similar to the trunk circuits of like designation disclosed in detail in the aforementioned patent to J. Baumfalk et a1. and in the patent to R. B. Buchanan et al., No. 2,233,282, granted February 25, 1941.

Consider first the operation of the alarm apparatus MA in Fig. 2 on an alarm call over trunk TI. When either one of alarm relays I1I or I12 is operated, in the manner described in the aforementioned patent to J. N. Walters, a cirtacts of relays I95 and I85 and the windings of T relay I and I95, to battery at the back contacts of relays I86 and I98, relay I86 being normal if trunk circuit TCI is idle and relay I 96 being normal if trunk circuit TC5 is idle. Whichever of relays I 85 and I95 operates first, it locks and opens the circuit for operating the other. If relay I85 operates, it connects the secondary winding of transformer I18 in series with the upper winding of relay I81, across conductors I8I and I82 and connects supervisory relay I14 to conductor I84. If relay I95 operates, it connects the, right winding of transformer I10 in series with the upper winding of relay I91, across conductors I9I and I92 and connects supervisory relay I14 to conductor I94.

Assuming that an operation of relay I13 causes the operation of relay I85, the connection of the right winding of transformer I10 across conductors NH and I82 causes the operation of relay I81 of the alarm apparatus and the operation of relays 14 and of trunk circuit TCI. Relay 98 closes a circuit for operating relay 81. Relay 81 closes circuits for operating relays 82 and 86, connects ground potential to conductor I83 to operate relay I86 and hold relay I81, and connects ground potential to conductor 53 to prevent seizure of trunk circuit TCI by a selector SI. Relay 86 also connects ground potential to conductors 53 and I83 and closes a circuit for operating relay 82. With relays 98 and 82 operated, the upper winding of polarized relay 84 is bridged across the conductors of trunk TI to operate the line relay (not shown) of the trunk circuit T02, the current through the upper winding of relay 84 being in the nonoperating direction. The aforementioned operation of relay 14 in series with relay 99 connects ground to conductor 53 and, relay 86 havin been operated, opens the operating circuit of the normally operated relay 88. Relay 88 is slow in releasing so as tovmaintain the bridge across the conductors of trunk TI for a long enough time to prepare the incoming selector IS in the tandem office for response to impulses. When relay 88 releases, it opens the bridge across the conductors of trunk TI, closes a circuit for operating relay 89, and connects ground to conductors 53 and I 83. The operation of relay 89 short-circuits the winding of relay 14 to cause its release, recloses the bridge across trunk TI, and prevents the reoperaticn of relay 88 until the connection is released. The momentary opening of the bridge across trunk TI, due to the release of relay 88 and operation of relay 89, causes the brushes of the selector IS in the tan dem office to be stepped up to the first level of its bank and to be advanced in this level to select an idle trunk to the master office, in the manner set forth in detail in the aforementioned patent to J. Baumfalk et a1.

If the selector IS fails to find an idle trunk to the master office, the brushes are advanced to an eleventh rotary position in the manner described in the forementioned 2nd edition of Automatic Telephony to transmit a busy tone over trunk TI to ofiice LO. Since the call is a trouble alarm call, this busy tone is without efiect. To enable release of the trunk TI and selector IS so that a second alarm call can be made, the aforementioned operation of relay I81 connects the winding of relay I9I to timing conductor H5; and, as soon thereafter as timing relays II I, H2 and H3 are normal, the connection of ground to conductor II5 causes the operation of relay I8I. Relay IBI locks under control of relays I93, I81 and lease of relay 90 of trunk circuit TCI.

I00, connects ground to. start conductor III] to cause the operation of timing relay I I I', and connects the winding of relay I03 to timing conductor H4. Relay III disconnects ground from conductor H and closes the circuit for energizing relay I I2; Relay H2 is slow in operating and operates from two to four minutes after its energizing circuit is closed. Relay H2 closes the circuit for operating relay H3. The operation of relay H3 causes the release of relay III; the release of relay III causes the release of relay H2; and the release of relay H2 causes the. release of relay H3, thereby reconnecting the winding of relay I I I to start conductor H0.. Relay H3 is slow in releasing and, while operated, it connects ground to conductor II4 to cause the operation of relay I03. Relay I03 locks under control of relays I51 and I00, releases relay IOI, releases relay I85, and opens the bridge across conductors l8l and I82, thereby causing the re- Relay I8I is rendered somewhat slow in releasing due to the connection of resistor I02 in parallel with its winding so as to insure closure of the locking circuit of relay I03 before the operating circuit of relay I88 is opened. The release of relay 98 opens the bridge across the conductors of trunk TI, to cause the return of the trunk circuit T02 and selector IS to normal, and causes the successive release of relays 81, 86, 82 and 89 and reoperation of relay 88. With relays 14, 85 and 81 released and relay 88 reoperated, ground is disconnected from conductors 53 and I83, thereby releasing relays I86 and I81. The release of relay I 81 causes the release of relay I03, relay I03 being slow in releasing to insure return of the trunk and selector circuits in the tandem office to normal before trunk TI can again be seized. With relay I13 held operated by one of alarm relays HI and I12, relay I85 reoperates and the trunk TI is again seized to initiate another alarm call. I

If on the above-described alarm call the selector IS finds an idle trunk to the master ofiice, the trunk circuits TC3 and T04 are effective in the manner described in the aforementioned patent to J. Baumfalk et al. and J. N. Walters to operate a calling signal L associated with jack J at an operators position. When the call is answered, the trunk circuit TC4 transmits an answering signal to the trunk circuit TC3, the trunk circuit TC3 thereupon transmits an answering signal to the trunk circuit TC2, and the trunk circuit TC2 reverses the current through the conductors of trunk TI to effect the operation of the polarized supervisory relay 84 all in the manner described in the aforementioned pat-- ent to J. Baumfalk et a1. and J. N. Walters. Relay 84 closes a circuit for operating relay 13.

Relay 13 closes a circuit for holding relay 81 operated independent of the continued operation of relay 90 and connects ground to conductor I84 to operate relays I14 and I00. Relay I16 does not operate since its winding is short-circuited. Relay I14 locks under control of the op erated one of alarm relays HI and I12 and closes a circuit through the left Winding of transformer I and the left winding of tone supply transformer LTI to transmit a trouble tone to the answering operator in the master office. When F the operator releases the connection, the current through the conductors of trunk TI is again reversed in the manner described in the aforementioned patent to J. Baumialk et al. to cause the release of relay 84. The release of relay 84 causes the release of relay 13, thereby disconnecting ground from conductor I84 to open the short circuit around the winding of relay I16. Relay I16 operates and is held operated under thecontrol of the operated one of alarm relays Ill and I12 to prevent the initiation of a second alarm call to the master office. The operation of relay I16 releases relay I85, thereby opening the bridge across conductors I8I and I82 to cause the release of relay 90 of trunk circuit TCI. The release of relay 90 causes the successive release of relays 01, 86 and 82, ground being thereby disconnected from conductor 53 to render the trunk circuit TC I selectable, and from conductor I83 to cause the release of relays I86 and I81.

If relay I is operated, due to the operation of relay I13, the trunk circuit TC5 is seized to initiate an alarm call; and in this case relays I86 and I81 function as do relays I86 and I81 on an alarm call through trunk circuit TCI, as above described.

It is to be noted that whenever trunk circuit TCI is busy, relay I66 is operated by ground potential connected to conductor I83 to prevent the operation of relay I85; and that whenever trunk circuit T02 is busy, relay I96 is operated by ground potential connected to conductor I93 to prevent the operation of relay I95.

Referring now to the alarm apparatus MA shown in Fig. 3, relay I05 of the trunk release circuit is operated through conductor I04, in series with the one or the other of relays I85 or I95, upon operation of relay I13. An alarm call is thereby initiated over trunk TI or trunk T5 as above described. Relay I05 connects the winding of relay I06 to timing conductor H5; and, as soon thereafter as timing relays III, H2 and H3 are normal, relay I96 operates. Relay I06 locks under the sole control of relay I05, closes a circuit for holding relay I05 and the operated one of relays I 85 and I95 under control of timing relay I I3, and connects ground to start conductor H6 to cause the timing relays to repeat their cycle of operations. If the alarm call is not answered, or the incoming selector in the tandem ofiice encounters an all-trunks-busy condition, so that the relay I14 is not operated, the operation of relay H3, from two to four minutes after the operation of relay I06, disconnects ground from conductor H6 to cause the release of relay I05 and the release of the operated one of relays I85 and IE5. The release of the operated one of relays I85 and I95 causes the release of the associated one of trunk circuits TC I and TC5 and the release of the associated incoming selector in the tandem ofiice. As soon as the operated one of relays I86 and I96 releases and relay H3 also releases, relay I85 or relay I65 will be operated to originate a new alarm call.

What is claimed is:

1. In a telephone system, an unattended cflice, trunks for use on calls from the unattended ofiice to a master oflice, means in said unattended office responsive to a trouble condition therein for seizing an idle one of said trunksto initiate an alarm call to an operator in the master office. means associated with the seized trunk responsive to the answer of the call and the subsequent release of the connection by the answering operator in the master office for releasing the trunk in the unattended office, and means in the urn attended ofilce eifective if an alarm call is not answered within a predetermined interval of time for automatically causing release of the trunk over which the alarm call is being made.

2. In a switching system, outgoing trunks, means for seizing an idle one of said trunks, means associated with a seized trunk operatively responsive to an answering signal incoming over the trunk, and means eifective only if no answering signal is received within a predetermined interval of time after a trunk is seized for automatically causing the release of said trunk.

3. In a telephone system, an unattended local office, a tandem unattended office, a master office, trunks between said unattended oifices, a group of trunks between said tandem and master offices, selectors in said tandem ofiice, each selector individual to one of the first-mentioned trunks and all of said selectors having access in common to said group of trunks to the master office, means in the local office for seizing an idle trunk to the tandem oflice and for automatically causing the operation of the associated selector in the tandem ofiice to select the group of trunks to the master ofice and an idle trunk therein, means comprising a calling signal in the master office associated with the selected trunk and actuated responsive to seizure by said selector, means effective if all of the trunks in said group are busy for operating said selector to an overflow position, means for answering 'a call in the master ofiice, means in the local ofiice responsive to the answer of a call to the master oflice, and

means in the local office automatically effective if a call to the master ofiice is not answered within a predetermined interval after seizure of a trunk to the tandem office for releasing the trunk to the tandem ofiice.

4. In a telephone system, an unattended oifice', I

trunks for use on calls from the unattended ofiice to a master ofiice, means in said unattended ofiice responsive to a trouble condition therein for seizing an idle one of said trunks to initiate an alarm call to an operator in the master office, means associated with a seized trunk effective if the call is not answered within a predetermined interval after seizure for automatically effecting release of the trunk, and means associated with said trunk in the unattended omce responsive to answer of the call in the master oilice for preventing said automatic release of the trunk. 1

5. In a telephone system, an unattended ofiice, trunks for use on calls from the unattended office to a master office, means in said unattended means in said unattended oflice comprising a relay individual to a seized one of said trunks and timing means common to said trunks for automatically effecting release of the trunk if the call is not answered within a predetermined interval of time, and means associated with said trunks in the unattended oiiice responsive to answer of an alarm call to the master ofiice for preventing the automatic release of the trunk used on the call.

6. In a telephone system, an unattended office, trunks for use on calls from the unattended office to a master office, means in said unattended ofi'ice responsive to a trouble condition therein for seizing an idle one of said trunks to initiate an alarm call to an operator in the master ofiice, means in said unattended ofiice and common to said trunks for automatically effecting release of a seized trunk if the call is not answered within a predetermined interval of time, and means associated with said trunks in the unattended oiiice responsive to answer of an alarm call to the master ofiice for preventing the automatic release of the trunk used on the call.

7. In a telephone system and combination according to claim 4, means associated with said trunks in the unattended office responsive to release of an alarm call by the answering operator in the master office for effecting release of the trunk used on the call and for preventing seizure of a trunk to initiate another alarm call as long as the same trouble condition continues to exist in the unattended ofiice.

8. In a telephone system and combination according to claim 5, means associated with said trunks in the unattended office responsive to release of an alarm call by the answering operator in the master oflice for effecting release of the trunk used on the call and for preventing seizure of a trunk to initiate another alarm call as long as the same trouble condition continues to exist in the unattended ofiice.

9. In a telephone system and combination according to claim 6, means associated with said trunks in the unattended ofiice responsive to release of an alarm call by the answering operator in the master office for effecting release of the trunk used on the call and for preventing seizure of a trunk to initiate another alarm call as long as the same trouble condition continues to exist in the unattended office.

10. In a telephone system and combination according to claim 4, means responsive to the automatic release of a trunk on an alarm call to the master oifice for immediately effecting reseizure of said trunk to initiate another alarm call.

11. In a telephone system and combination according to claim 4, means associated with said trunks in the unattended ofiice responsive to release of an alarm call by the answering operator in the master ofiice for effecting release of the trunk used on the call and for preventing seizure of a trunk to initiate another alarm call as long as the same trouble condition continues to exist in the unattended oflice, and means responsive to the automatic release of a trunk on an alarm call to the master oflice for immediately effecting reseizure of said trunk to initiate another alarm call.

12. In a telephone system, an unattended local oifice, a tandem unattended oflice, a master oflice, trunks between said unattended oflices, a group of trunks between said tandem and master offices, selectors in said tandem office, each selector individual to one of the first-mentioned trunks and all of said selectors having access in common to said-group of trunks to the master ofiice, means in the local office for seizing an idle trunk to the tandem office and for automatically causing the operation of the associated selector in the tandem oflice to select the group of trunks to the master oflice and an idle trunk therein, means comprising a calling signal in the master office associated with the selected trunk and actuated responsive to seizure of said selector, means for answering a call in the master omce, means in the local ofilce responsive to the answer of a call to the master oflice, and means in the local ofiice automatically effective if a call to the master office is not answered within a predetermined interval after seizure of a trunk to the tandem oflice for releasing the trunk to the tandem ofiice.

THOMAS L. DIMOND. 

